Pharmacy & Therapeutics - September 2008 - (Page 533)

Copays and Oral Antidiabetic Drugs and January 31, 2005 (the intake period). The date of the first pharmacy script for an OAD within the intake period was defined as the index date. Patients 18 years of age or older were included if they had at least one prescription for an OAD and one or more medical claims for type-2 diabetes with an International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code of 250.x with a fifth digit of “0” (type-2 or unspecified type, not stated as uncontrolled) or “2” (type 2 or unspecified type, uncontrolled) during the intake period. To be eligible for the study, patients had to be newly initiated on an OAD as monotherapy and were not permitted to have any prescriptions for another OAD or insulin in the six months before the index date. The cohort was grouped according to the class of OAD received: biguanides, sulfonylureas, thiazolidinediones (TZDs), or others (including meglitinide analogues and alpha-glucosidase inhibitors). Patients also had to be continuously eligible for their health plan’s pharmacy and medical benefits for at least six months before and 12 months after the index date. Patients were excluded from the study if they used multiple OAD medications on the index date, including OADs in a single formulation; if they were enrolled in Medicaid; or if claims showed that they missed a copayment or if days’ supply data for the index fill was missing. Patients were followed for 12 months after the index date to determine prescription copays, OAD treatment patterns, and HbA1c values. tion of treatment was calculated using the fill dates and days’ supply data from each prescription in the pharmacy claims records. Subjects were considered to be undergoing continuous treatment if they had a subsequent fill by the end of the allowable refill window, calculated as two times the day’s supply of the prior fill. It was assumed that patients were at least 50% compliant with each fill. Patients were considered to have discontinued treatment if they did not obtain a refill for the index drug by the end of their allowed refill window. The discontinuation date was then defined as the date of the last fill plus two times a day’s supply. Subjects were considered to have switched to a new drug if they had a fill for a drug other than their index drug and if they had no subsequent refills for that index drug after the new drug fill. Patterns were monitored for switching both to a new drug within the same class and to a new drug within a different class. The date of first switch was the date of the first fill for the new drug. Augmentation of index treatment was defined as a fill for a new drug within a different class from that of the index class with subsequent refills for the index drug after the new drug fill. The date of first augmentation was the date of the first fill for the new drug of a different class. Patients were followed for one year, and their data were censored at the end of the study if they did not discontinue treatment, switch to another medication, or add a drug to therapy. We presented the descriptive results for time to treatment failure at the copay level. Copay was a continuous variable in the Cox proportional hazards model, which we used to analyze the impact of copay on time to treatment failure (discontinuing or switching to another therapy). OUTCOME METRICS Demographic and Clinical Data Each patient’s age and sex were recorded from the health plan enrollment information at the index date along with the provider’s specialty associated with the index prescription and geographic region. We analyzed pre-index (baseline) comorbidities using ICD-9-CM, Current Procedural Terminology (CPT), or Healthcare Common Procedure Coding System (HCPCS) codes for hypertension, dyslipidemia, nephropathy, neuropathy, retinopathy, ischemic heart disease, prior angina, congestive heart failure, peripheral vascular disease, cerebrovascular disease, obesity, and amputations found in the medical claims of patients during the six months prior to the index date (Table 1). Descriptive statistics were presented for the most commonly occurring comorbidities. We determined the Deyo– Charlson Comorbidity Index (DCI)19 score for each patient for the six months prior to the index date. Adherence We measured adherence using data from prescription pharmacy claims to determine the medication possession ratio (MPR).5,20 The MPR was defined as the number of days for which a patient had a supply of the index OAD during the year after the index fill, divided by 365 days. Results were presented by copay level for descriptive analyses. For multivariate analyses, we included copay as a continuous variable. Clinical Outcomes for Hemoglobin A1c For a subset of the cohort, electronic laboratory data were available. Outpatient HbA1c values were captured via a national laboratory provider for the subset of patients with measurements available during the pre-index period, the post-index period, or both. Copays We collected the index fill copay for each patient, reflecting a 30-day supply of medications. The mean copay was described for each OAD class and for descriptive presentation. Results were stratified by four copay levels: less than $10, between $10 and $20, between $20 and $30, and $30 or more. Within multivariate analyses, copay was analyzed as a continuous variable. STATISTICAL ANALYSIS Descriptive statistics were presented as means (± standard deviation [SD]) and as relative frequencies. A Cox proportional hazards model was used to evaluate whether drug copay, as a time-varying covariate, was a predictor of treatment failure (i.e., therapy discontinuation or a switch of the index OAD) after we adjusted for age, sex, provider specialty, geographic region, health insurance type, pre-index Deyo–Charlson Index (DCI) score, number of unique medications, use of insulin in the post-index period, and pre-index comorbidities (hypertension, dyslipidemia, nephropathy, neuropathy, retinopathy, Treatment Patterns Although patients tended to experience multiple modifications to their treatment regimen in their first year of therapy, only the first treatment modification was recorded. The dura- Vol. 33 No. 9 • September 2008 • P&T® 533

Table of Contents Feed for the Digital Edition of Pharmacy & Therapeutics - September 2008

Pharmacy & Therapeutics - September 2008 Contents Editorial Medication Errors Prescription: Washington New Drugs/Drug News/New Medical Devices Drug Forecast Effect of Prescription Copays on Adherence and Treatment Failure with Oral Antidiabetic Medications Vaccine Declinations Present New Challenges for Public Health Universal Health Care in America Digestive Disease Week and American Diabetes Association Pharmaceutical Approval Update

Pharmacy & Therapeutics - September 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.